I've used shells collected from the beach in my aquariums without
problems. I usually rinse them well and then boil them to get rid of any
nasties before I drop them in the tank.

Gabrielle

not very clever wrote:
I have a new pond (approx 5000 litres) with a pump/filter system with a
capacity up to 12000 litres.

I intend keeping Goldfish in it once everything is balanced out.

Would seashells (cockle) be okay in the base? I have read somewhere that
they are made of calcium which might be a problem - or would the filter sort
that out?

Thanks for your help:-)